The present invention relates to a vehicle transmission for use in conjunction with self-propelled vehicles which turn on a very small radius or zero radius and, in particular, to such transmissions which selectively and independently link both forward and reverse drive to a pair of drive wheels for the vehicle.
Vehicles of the type which are commonly referred to as zero turning radius vehicles have become quite popular for various purposes especially mowing where it is sometimes necessary for the mower to make quite sharp turns. For example, mowers of this type are used for mowing about headstones in a cemetary wherein a number of sharp turns must be made in order to be able to cut all the grass. The zero turning radius mowers also significantly reduce the time required to mow a particular region as compared to conventional mowers that do not have the zero turning radius ability.
In order to provide for zero turning radius capability in a mower or the like, it is necessary to allow the operator the ability to independently control the forward and reverse speeds on at least a pair of the drive wheels for the vehicle. In this manner, the operator can, for example, stop the left drive wheel and have the right drive wheel go forward such that the vehicle pivots about the left drive wheel and, thus, effectively turns on a "zero radius". Prior zero turning radius vehicles have typically required a sophisticated transmission mechanism for allowing the operator to selectively transfer power to the drive wheels.
A common method of independently driving the rear wheels in the past has been to provide independent hydraulic transmissions for each of the drive wheels of the vehicle. While such transmissions are effective in producing a zero turning radius capability, they can also be quite expensive, or quite complex and are prone to breakdowns of the type that cannot be repaired by a typical user of the mower, thereby requiring the user to return the transmissions to a specialized dealer for repair.
Consequently, it is desirable to have a relatively simple mechanical apparatus which is comparatively easy to repair and relatively inexpensive as compared to prior devices of this type and yet which function highly effectively as a transmission for use in conjunction with zero turning radius vehicles. It is also desirable to provide such a transmission which provides a degree of dampening to prevent jerky motion and which effectively returns the controls to neutral, should be user's hands leave the control mechanisms for the apparatus, thereby reducing the chance of injury to the user should the user fall from the machine or the like.